AUTHOR=Chen Ke , Zhurbenko Peter , Danilov Lavrentii , Matveeva Tatiana , Otten Léon 

TITLE=Conservation of an Agrobacterium cT-DNA insert in Camellia section Thea reveals the ancient origin of tea plants from a genetically modified ancestor

JOURNAL=Frontiers in Plant Science

VOLUME=13

YEAR=2022

URL=https://www.frontiersin.org/journals/plant-science/articles/10.3389/fpls.2022.997762

DOI=10.3389/fpls.2022.997762

ISSN=1664-462X

ABSTRACT=<sec><title>Introduction</title><p>Many higher plants contain cellular T-DNA (cT-DNA) sequences from <italic>Agrobacterium</italic> and have been called “natural genetically modified organisms” (nGMOs). Among these natural transformants, the tea plant <italic>Camellia sinensis</italic> var. <italic>sinensis</italic> cv. Shuchazao contains a single 5.5 kb T-DNA fragment (CaTA) with three inactive T-DNA genes, with a 1 kb inverted repeat at the ends. <italic>Camellia</italic> plants are allogamous, so that each individual may contain two different CaTA alleles.</p></sec><sec><title>Methods</title><p>142 <italic>Camellia</italic> accessions, belonging to 10 of 11 species of the section <italic>Thea</italic>, were investigated for the presence of CaTA alleles.</p></sec><sec><title>Results discussion</title><p>All accessions were found to contain the CaTA insert, showing that section <italic>Thea</italic> derives from a single transformed ancestor. Allele phasing showed that 82 accessions each contained two different CaTA alleles, 60 others had a unique allele. A phylogenetic tree of these 225 alleles showed two separate groups, A and B, further divided into subgroups. Indel distribution corresponded in most cases with these groups. The alleles of the different <italic>Camellia</italic> species were distributed over groups A and B, and different species showed very similar CaTA alleles. This indicates that the species boundaries for section <italic>Thea</italic> may not be precise and require revision. The nucleotide divergence of the indirect CaTA repeats indicates that the cT-DNA insertion took place about 15 Mio years ago, before the emergence of section <italic>Thea</italic>. The CaTA structure of a <italic>C. fangchengensis</italic> accession has an exceptional structure. We present a working model for the origin and evolution of nGMO plants derived from allogamous transformants.</p></sec>